Welcome to Fishlore, Mark (I don't think I've greeted you before this)

Your fish would do fine fasting for five days, but they don't have to.
If you're not willing to buy a high-price feeding machine, throw that idea out the window. I've heard of the machines having their timers give out, and the machine either stops working altogether or, worse, dumps the entire contents out in one day.
I would avoid the
chalk feeder blocks. There seems to be little control in the size of the pellets in the block. Sometime last year, a member lost a fish that had something lodged in its intestines (it's a pretty gruesome story. Just believe me when I say that there is no doubt about this). The member found that the chalk feeder block had little pellets of food that expanded a bit as they got wet.
The
gel blocks seem to be better, as they seem to break down into little bits of flaky food, bloodworms, and the like. This is the route I'm going to take if I'm ever gone long enough that I feel like I need to feed my tanks. What I'll do in these cases, however, is buy two of the blocks and dissect one of them to make sure that it doesn't have anything too big for my fish to eat.